Semiconductor wafer processing requires an environment virtually free from AMC and particulate matter so the wafers may be processed without being contaminated. Accordingly, semiconductor processing is performed in clean rooms in which air is highly purified or filtered prior to its introduction into the room. Chemical filters as well as high efficiency particulate air (HEPA) and/or ultra low penetration air (ULPA) filters are commonly employed to filter and purify the air prior to its introduction into the clean room. As wafer processing enters into nano technology, more and more chemical filters are required to meet the tight AMC specification requirements for wafer processing.
FIG. 1 is a block diagram of the air flow in a conventional air filtration system 100 for a clean room. As shown in FIG. 1, the conventional air filtration system 100 introduces air into the clean room 114 in two ways: (1) through a make-up air flow 102 and (2) through a recirculation airflow 122. The make-up airflow 102 takes air from an external (e.g., outdoor) air supply 104 and passes it through a make-up air treatment unit (ATU) 106. In the ATU 106, the outdoor air undergoes airborne molecular contamination (AMC) removal treatment by passing through one or more chemical filters. After passing through ATU 106, the make-up airflow 102 is mixed with air from the recirculation flow 122. The combined airflow is cooled through dry cooling coil 108.
The combined airflow, which includes the filtered outdoor air and the recirculated air, is passed through a fan filter unit (FFU) 110 where it is once again filtered by one or more chemical filters. The combined air is then blown by the fan of the FFU 110 into the clean room 114. A fan mounted on the tool directs air from the clean room 114 into the tool environment 112. A portion of the air that passes through the tool environment 112 is dispersed back into the clean room 114 where it mixes with the air in the clean room 114. The mixed air flows into a sub-fabrication air return area 116. At the sub-fabrication air return area 116, part of the returned air will be discharged to the outdoors, along with some air drawn directly from the tool environment 112, after passing through the air abatement system 118. The remaining portion of the airflow will be recirculated and mixed with the make-up flow 102 from the outdoors at the dry cooling coil 108. The conventional air purification systems as described above are expensive as they require a large quantity of expensive chemical filters to purify both the make-up airflow 102 and the recirculation airflow 122. Additionally, the conventional systems suffer from cross-contamination between the clean room and the tool environment caused by turbulent air in the clean room 114.
Accordingly, an improved air filtration system for nano-wafer environments is desired.